Control of a pressure exchanger by displacement of an injection valve member

ABSTRACT

A device for injecting fuel into a combustion chamber of an internal combustion engine, including an injector body which contains an injection valve element which can be actuated through pressurization/pressure relief of a control chamber by means of a control valve. A pressure booster having a piston unit that divides a working chamber from a control chamber of the pressure booster acts on a compression chamber that communicates with a nozzle chamber encompassing the injection valve element. A pressurization or pressure relief of the control chamber of the pressure booster occurs as a function of the stroke motion of the injection valve element.

TECHNICAL FIELD

Both pressure-controlled and stroke-controlled injection systems can beused to supply fuel to combustion chambers of autoignition internalcombustion engines. In addition to unit injectors and unit pumps,accumulator injection systems are also used as fuel injection systems.Accumulator (common rail) injection systems advantageously make itpossible to adapt the injection pressure to the load and speed of theautoignition internal combustion engine. Achieving high specific outputsand reducing emissions of the autoignition engine generally require thehighest possible injection pressure.

PRIOR ART

For strength reasons, the achievable pressure level in accumulatorinjection systems currently in use is limited to approximately 1600 barat this time. In order to further increase the pressure in accumulatorinjection systems, common rail systems employ pressure boosters.

DE 199 10 970 A1 relates to a fuel injection apparatus. This fuelinjection apparatus has a pressure booster unit, which is disposedbetween a pressure accumulator and a nozzle chamber and whose pressurechamber is connected to the nozzle chamber via a pressure line. Inaddition, a bypass line is provided, which is connected to the pressureaccumulator. The bypass line is connected directly to the pressure line.The bypass line can be used for a pressure injection and is disposedparallel to the pressure chamber so that the bypass line is continuouslyindependent of the movement and position of a moving pressure fluid inthe pressure booster unit. This feature increases the flexibility of theinjection. A differential chamber can be connected to a leakage line viaa 2/2-way valve and there is a connection from the differential chamberto the pressure accumulator. A valve device, which is disposed outsidethe injector at an arbitrary point between the pressure accumulator andthe injector, is associated with the pressure booster unit in order tocontrol it.

DE 190 40 526 A1 also relates to a fuel injection apparatus. This fuelinjection apparatus has a pressure booster unit, which is disposedbetween a pressure accumulator and a nozzle chamber and has a movingpiston unit for boosting the pressure of the fuel to be supplied to thenozzle chamber. In order to control the pressure booster unit, thepiston unit has a transition from a larger piston cross-section to asmaller piston cross-section and a differential chamber formed as aresult of this. The differential chamber is connected to the pressureaccumulator by means of a filling path that contains a filling valve.This permits a reduction of the control quantity during the triggeringof the pressure booster unit and permits a rapid resetting of the pistonunit.

In view of ever-increasing standards regarding emissions and noiseproduction in autoignition internal combustion engines, further stepsmust be taken in the injection system in order to meet the stricterlimit values to be expected in the near future.

DEPICTION OF THE INVENTION

With the design proposed according to the invention, it is possible tocontrol a fuel injector of a fuel injection system with an actuator,which makes it possible to significantly reduce the complexity and costsof production. In particular, the design proposed according to theinvention makes it possible to produce a pressure booster by makingdirect use of the movement of an injection valve element advantageouslyembodied as a nozzle needle, thus eliminating the need for a separateactuator. The pressure booster can be switched on with the openingmovement of the injection valve element. The pressure booster contains apiston unit, which separates the working chamber of the pressure boosterfrom its control chamber and can be set with a partial stroke, thepassage of which permits the pressure booster to be switched on. Thisachieves considerable advantages with regard to the design of a fuelinjector with a pressure booster. For example, it is possible to executemultiple preinjections into the combustion chamber of an autoignitioninternal combustion engine without activating the pressure booster. Itis therefore possible to execute a preinjection, which occurs at apressure level that essentially corresponds to the pressure levelprevailing inside a high-pressure accumulator (common rail). After thepiston unit of the pressure booster has traveled its set strokedistance, a main injection can be executed with an activated pressurebooster, thus resulting in the production of a high pressure levelduring the main injection, which has a favorable effect on the emissionsof autoignition internal combustion engines and is higher than thepressure prevailing inside a high-pressure accumulator (common rail).This makes it possible to achieve a boot-shaped injection since thefirst injection phase (preinjection phase) occurs at a lower pressureand then a pressure increase to the boosted injection pressure occurs.The activation of the pressure booster can produce a pressure increaseup to the maximal permissible pressure during the main injection phasewhen the injection valve element is in the open position. Furthermore,the design proposed according to the invention makes it possible toachieve the pressure booster before the closing of the injection valveelement that is preferably embodied as a nozzle needle, which makes itpossible to prevent pressure surges above the maximal injection pressurewhen the needle closes. This has a favorable effect on the service lifeof the fuel injection system in an autoignition internal combustionengine. In addition, the design according to the invention can execute asecondary injection phase at a very high injection pressure after themain injection phase, as well as a stepped secondary injection thatfollows the main injection by a somewhat longer time span.

DRAWINGS

The invention will be explained in detail below in conjunction with thedrawings.

FIG. 1 shows an embodiment version of a pressure booster actuated by aninjection valve element in a first state,

FIG. 2 shows the embodiment version of the design proposed according tothe invention according to FIG. 1, with a pressure booster in a secondstate,

FIG. 3 shows another embodiment version of a pressure booster that canbe actuated by an injection valve element, with two valve elementsguided one inside the other, and

FIG. 4 shows an embodiment version of a pressure booster actuated by aninjection valve element, with two valve elements, one of which isspring-loaded.

EMBODIMENT VERSIONS

FIG. 1 shows a first embodiment version of a pressure booster that canbe actuated by an injection valve element, depicted in a first state inwhich the control chamber of the pressure booster is disconnected fromthe return, i.e. from the low-pressure region of the fuel injectionsystem.

Starting from a high-pressure source 1, which can be embodied, forexample, as a high-pressure accumulator (common rail), a high-pressureinlet 2 extends to a pressure booster 3. The high-pressure inlet 2 has ahigh-pressure line 7 that can contain a check valve 8. Parallel to thehigh-pressure line 7, the high-pressure inlet 2 from the high-pressuresource 1 acts on a parallel branch 11 that can contain a filling valve10. Another branch 12 extends parallel to it, which contains a throttlerestriction 13. The first parallel branch that contains the fillingvalve 10 and the additional parallel branch 12 that contains thethrottle restriction 13 feed into a control chamber 15 of the pressurebooster 3. The pressure booster 3 also has a working chamber 14, whichlikewise communicates with the high-pressure source 1 via thehigh-pressure inlet 2.

A piston unit 17 separates the working chamber 14 and the controlchamber 15 inside the pressure booster 3. The piston unit 17 can becomprised of one piece or of multiple parts and has a section with alarger diameter, whose end surface delimits the working chamber 14 ofthe pressure booster 3, and a piston part with a smaller diameter thanthis, whose lower end surface delimits a compression chamber 18 of thepressure booster 3. The compression chamber 18 of the pressure booster 3has a compression line 20 extending from it, which at its other end,unites with the high-pressure inlet 7 that contains the check valve 8and transitions with it into a nozzle chamber inlet 9. The controlchamber 15 of the pressure booster 3 contains a spring element 16, whichacts on an underside of the piston unit 17 and is supported against thebottom of the control chamber 15. The pressure booster 3 is disposedinside the injector body 5; the control chamber 15 of the pressurebooster 3 has a control line 19 that is in turn connected to an annularchamber 33 of a valve element 27.

The nozzle inlet 9, which is fed by both the high-pressure line 7 andthe compression line 20 extending from the compression chamber 18, feedsinto a nozzle chamber 36 at a junction point 37.

A high-pressure branch 22 that contains an inlet throttle element 23branches off from the nozzle chamber inlet 9. The high-pressure branch22 feeds into a control chamber 21 inside a nozzle body 6 of the fuelinjector 4. The control chamber 21 can be pressure-relieved by means ofa control valve 25 embodied as a 2/2-way valve. An outlet throttleelement 24 is provided between the control valve 25 (2/2-way valve) andthe control chamber 21. A low-pressure return 26 extends from thelow-pressure side of the control valve 25 (2/2-way valve) and feeds intoa fuel tank, not shown here, of a motor vehicle. The control valve 25can be either a solenoid valve or as a valve that is actuated by apiezoelectric actuator. In addition, the control valve 25 can also beembodied as a servo valve or as a valve that can be actuated directly.

The fuel injector 4 shown in FIG. 1 has an injection valve element 34,which is advantageously embodied as a nozzle needle. In the embodimentversion according to FIG. 1, the injection valve element 34 is acted onby a one-piece valve element 27, which can be embodied as a valvepiston. The end surface 29 of the one-piece valve element 27 delimitsthe control chamber 21, which can be filled via the inlet throttlerestriction 23 and can be pressure-relieved via the outlet throttlerestriction 24. Under the control chamber 21, the one-piece valveelement 27 embodied as a valve piston is encompassed by an annularchamber 33 into which the control line 19 feeds, which connects theannular chamber 33 to the control chamber 15 of the pressure booster 3.The annular chamber 33 is provided with a control edge 31 thatcooperates with a control edge 30 provided on the one-piece valveelement 27. In the depiction according to FIG. 1, the control edges 30and 31 overlap each other by a stroke distance h₁, see reference numeral32. Below the one-piece valve element 27, the nozzle body 6 containsanother hydraulic chamber that has a second low-pressure return 26.2branching from it, which also leads to the fuel tank of the motorvehicle, not shown in FIG. 1.

The nozzle chamber inlet 9 acts on the nozzle chamber 36 of the fuelinjector 4 inside the nozzle body 6 with highly pressurized fuel so thata hydraulic force is generated, which acts in the opening direction on apressure shoulder 35 provided on the circumference surface of theinjection valve element 34. Starting from the nozzle chamber 36 insidethe nozzle body 6, an annular gap 38 extends to a seat 40 of theinjection valve element 34 at the end oriented toward the combustionchamber. Under the seat 40 at the end oriented toward the combustionchamber, injection openings 39 are provided, which can be embodied, forexample, as annular rows of openings, in the form of one or morecircular arrangements of openings extending concentrically to oneanother. In the position of the injection valve element 34 shown in FIG.1, the injection openings 39 are closed by the injection valve element34, which has traveled into the seat 40 at the end oriented toward thecombustion chamber so that no fuel can flow into a combustion chamber 41of the autoignition internal combustion engine. In the depictionaccording to FIG. 1, the reference numeral 42 indicates the position ofthe injection valve element 34 in which it closes the injection openings39. No injection of fuel into the combustion chamber 41 of theautoignition internal combustion engine occurs in this position of theinjection valve element 34.

The fuel injection system has a number of fuel injectors 4 thatcorresponds to the number of cylinders of the autoignition internalcombustion engine; each of the fuel injectors 4 has a pressure booster 3and each fuel injector 4 is associated with a control valve 25. In theworking state shown in FIG. 1, i.e. when the injection openings areclosed 42, the control valve 25, which is preferably embodied as a2/2-way control valve, is in its closed position, i.e. the controlchamber 21 of the injection valve element 34 is disconnected from thelow-pressure return 26. The overlapping of the control edge 31 on thenozzle body 6 and the control edge 30 on the one-piece valve element 27closes the sliding seal constituted by the control edges 30 and 31. Theinjection valve element 34 is disposed in its position 42 that closesthe injection openings 39 at the end oriented toward the combustionchamber and the piston unit 17 of the pressure booster 3 ispressure-balanced so that no pressure boosting is taking place. In thisstate shown in FIG. 1, the filling valve 10 in the first parallel line11 that branches off from the high-pressure inlet 2 is open and thepiston unit 17 of the pressure booster 3 is disposed in its startingposition. The pressure prevailing inside in the high-pressureaccumulator (common rail), to name an example of a high-pressure source1, is connected via the open filling valve 10 to the back chamber 15 ofthe pressure booster 3 and travels via the check valve 8 contained inthe high-pressure line 7 to the control chamber 21 of the fuel injector4 as well as to its nozzle chamber 36. In this operating state, aninjection can occur at any time at the pressure level prevailing in thehigh-pressure source 1, i.e. the rail pressure level.

However, if the control valve 25, which can preferably be embodied as a2/2-way valve, is switched into its open position, then the controlchamber 21 is pressure-relieved via the outlet throttle 24 into thefirst low-pressure return 26.1 on the low-pressure side of the fuelinjector 4. Because of the dropping pressure in the control chamber 21of the fuel injector 4, the hydraulic forces acting on the pressureshoulder 35 of the injection valve element 34 predominate and theinjection valve element 34 opens. An injection of fuel into thecombustion chamber 41 of the autoignition internal combustion enginethrough the injection openings 39 at the end oriented toward thecombustion chamber begins at the pressure level supplied by thehigh-pressure source 1. Because of the series connection of theone-piece valve element 27 with the injection valve element 34, when anopening movement of the injection valve element 34 occurs, the endsurface 29 of the one-piece valve element 27 travels into the controlchamber 21 of the fuel injector 4. If this stroke motion exceeds thestroke distance h₁ (reference numeral 32), then the control edges 30 and31 are no longer in the state shown in FIG. 1, i.e. the overlappingstate, but are instead open so that the sliding seal is open. As aresult, the control chamber 15 of the pressure booster 3 is connected tothe second low-pressure return 26.2 via the control line 19 thatconnects the control chamber 15 to the annular chamber 33. Since thecontrol chamber 15 of the pressure booster 3 is now pressure-relievedinto the low-pressure region and the filling valve 10 closes, the pistonunit 17 of the pressure booster 3 is no longer pressure-balanced; as aresult, the pressure inside the working chamber 14 of the pressurebooster 3 predominates and the bottom end surface of the piston unit 17travels into the compression chamber 18. The piston unit 17 of thepressure booster 3 travels into the compression chamber 18 in accordancewith the pressure area ratios of this piston unit 17, thus supplying thenozzle chamber 36 with a boosted pressure—i.e. a higher pressure thancan be supplied to it by the high-pressure source 1 alone—via thecombustion chamber line 20, which feeds into the nozzle inlet 9 alongwith the high-pressure line 7 from the high-pressure source 1. When thelower end surface of the piston unit 17 travels into the compressionchamber 18, it compresses the fuel in the chamber so that a higher, i.e.boosted, pressure prevails in the nozzle chamber 36 via the nozzle inlet9.

When the stroke distance h₁ (reference numeral 32) is exceeded, then theinjection occurs at a boosted, i.e. higher, pressure. This makes itpossible to achieve a boot-shaped injection. The first injection phase,e.g. the preinjection phase, takes place at the pressure level suppliedby the high-pressure source 1, e.g. embodied in the form of ahigh-pressure accumulator (common rail), and is followed by anotherinjection phase at a significantly higher injection pressure level,which is generated a result of the pressure area ratios in the pistonunit 17 of the pressure booster 3 and is communicated via thecompression chamber line 20 to the nozzle chamber 36 contained in thenozzle body 6 of the fuel injector 4.

FIG. 2 shows the embodiment version of a fuel injector according to FIG.1, with a pressure booster in a second state.

FIG. 2 shows that the housing control edge 31 in the nozzle body 6 andthe control edge 30 of the one-piece valve element 27 are notoverlapping, which produces a low-pressure connection 50 between thecontrol chamber 15 of the pressure booster 3 via the control line 19,which into the annular chamber 33 that encompasses the one-piece valveelement 27. The control chamber 15 is thus pressure-relieved via thesecond low-pressure return 26.2 so that the piston unit 17, due to thepressure prevailing in the working chamber 14 of the pressure booster 3,compresses the fuel volume contained in the compression chamber 18 ofthe pressure booster 3 and conveys it via the compression chamber line20 and the nozzle inlet 9 into the nozzle chamber 36 of the nozzle body6. The injection valve element 34 of the fuel injector 4 is thendisposed in its retracted position 51, i.e. its open position, so thatfuel is injected via the nozzle chamber 36, the annular gap 38, and theopened injection openings 39 into the combustion chamber 41 of theautoignition internal combustion engine at a very high pressure, whichcorresponds to the pressure-boosted, increased pressure level.

In order to terminate the injection, the control valve 25, which ispreferably embodied as a 2/2-way valve, is closed so that a pressureincrease occurs in the control chamber 21 of the injection valve element34. Due to the action on the end surface 29 of the one-piece valveelement 27, the injection valve element 34 that cooperates with it movesin the closing direction. When the control edge 31 on the nozzle body 6is reached, the control edges 30 and 31 overlap each other so that thesliding seal they produce is closed. This closes the connection of thecontrol chamber 15 via the control line 19 and the annular chamber 33into the low-pressure return 26, thus deactivating the pressure booster3. The injection valve element 34 moves further in the direction of itsseat 40 at the end oriented toward the combustion chamber and thus at alater point, closes the injection openings 39 that feed into thecombustion chamber 41 of the autoignition internal combustion engine.Since the pressure booster 3 is already deactivated, pressure surgesthat occur with the closing of the injection valve element 34 arecompensated for.

The shut-off time of the pressure booster 3, i.e. the moment at whichthe control edges 30 and 31 overlap each other, can be optimally matchedto the end of the respective injection phase by adjusting the strokedistance h₁ (reference numeral 32) and the closing speeds of theinjection valve element 34 and the valve element 27. With smallinjection quantities, such as in a preinjection, the injection valveelement 34, which is preferably embodied as a nozzle needle, cannot becompletely opened along the entire stroke distance h₁ (reference numeral32), as a result of which the pressure booster 3 remains deactivated.Consequently, any number of preinjections can be executed without anactivated pressure booster 3. In preinjections for conditioning thecombustion mixture contained in the combustion chamber 41, thepreinjections are executed at the pressure level supplied by thehigh-pressure source 1, for example a high-pressure accumulator (commonrail), and not at the increased pressure level that can be achieved bymeans of the pressure booster 3. The number and duration of therespective preinjection phases, as well as the duration of the maininjection at an increased pressure level, can be set by adjusting thetriggering time of the control valve 25.

FIG. 3 shows another embodiment version of a pressure booster that isactuated by an injection valve element, with two valve elements guidedone inside the other.

The fuel injector 4 shown in FIG. 3, which is for supplying fuel to anautoignition internal combustion engine, also has a pressure booster 3integrated into the injector body 5. Via a high-pressure inlet 2, thehigh-pressure source 1 acts on a high-pressure line 7, a first parallelbranch 11, an additional parallel branch 12, and the working chamber 14of the pressure booster 3. The first parallel branch 11 contains afilling valve 10 and the additional parallel branch 12 contains athrottle restriction 13. The high-pressure line 7 contains a check valve8.

Analogous to the pressure booster 3 shown in FIG. 1, the pressurebooster 3 in the additional embodiment version in FIG. 3 has a pistonunit 17 that divides the working chamber 14 from the control chamber 15.The underside of the piston unit 17 acts on the compression chamber 18in the injector body 5 of the pressure booster 3 and, branching off fromthis compression chamber 18, the compression chamber line 20 leads tothe nozzle chamber inlet 9 and unites with the high-pressure line 7 fromthe high-pressure source 1.

By contrast with the embodiment version of the design proposed accordingto the invention shown in FIGS. 1 and 2, the injection valve element 34according to the depiction in FIG. 3 is acted on by a multi-part valveelement 28. The multi-part valve element 28 has a first valve element28.1 with an additional, second valve element 28.2 encompassing it. Thefirst valve element 28.1 and the additional valve element 28.2 can beembodied as piston-shaped. An annular surface 60 on the second valveelement 28.2 partially delimits the control chamber 21. The second valveelement 28.2 contains an opening 61 via which an end surface 62 of thefirst valve element 28.1 can be acted on by the pressure prevailing inthe control chamber 21. According to this embodiment version, a strokedistance h₁ (reference numeral 32) is established between the inner,first valve element 28.1, i.e. its end surface 62, and a collar at theopening 61 in the second valve element 28.2 of the multi-part valveelement 28. The second valve element 28.2 has a control edge 30 thatcooperates with a seat of a valve chamber 63. The control line 19 fromthe control chamber 15 of the pressure booster 3 feeds into the valvechamber 63 above the seat. A first return line 64 branches off from thevalve chamber 63 and leads to the low-pressure side of the fuel supplysystem. The first valve element 28.1 has a piston extension 66 that hasa smaller diameter than the piston part of the first valve element 28.1.The piston extension 66 passes through an additional cavity, which isdisposed underneath the valve chamber 63 in the nozzle body 6 andcontains a closing spring 67. The end surface of the piston extension 66rests against the end surface of the injection valve element 34, whichis preferably embodied as a nozzle needle.

When the pressure in the control chamber 21 is relieved by the controlvalve 25, which is preferably embodied as a 2/2-way valve, and thenozzle chamber 36 of the injection valve element 34 is acted on at thesame time, a hydraulic force builds up in the nozzle chamber 36 via thenozzle chamber inlet 9, which force acts on the pressure shoulder 35 ofthe injection valve element 34. The injection valve element 34 opens,thus allowing the execution, for example, of a preinjection via theinjection opening 39 into a combustion chamber, not shown here, of aninternal combustion engine. The preinjection, however, occurs only atthe pressure level prevailing in the high-pressure source 1 since thepressure booster 3 is not activated at this point. With furtherpressure-relief of the control chamber 21, the end surface 62 of theinner, first valve element 28.1 comes into contact with thecollar-shaped stop of the second, outer valve element 28.2 and carriesthe outer, second valve element 28.2 along with it in the openingdirection. As a result, the control edge 30 on the outer circumferenceof the second valve element 28.2 opens the connection of the controlchamber 15 to the first return line 64 via the control line 19 and thevalve chamber 63 so that the pressure in the control chamber 15 of thepressure booster 3 is relieved. The piston unit 17 of the pressurebooster 3 thus travels into the compression chamber 18 so that fuel isconveyed at an increased pressure via the compression chamber line 20,the nozzle chamber inlet 9, and the junction point 37 into the nozzlechamber 36 in the nozzle body 6. It is now possible to execute asubsequent injection into the combustion chamber of the autoignitioninternal combustion engine at an increased pressure level thatcorresponds to the pressure boosting of the pressure booster 3. Inaddition to the first return line 64 that branches off from the valvechamber 63, the additional embodiment version of a fuel injectoraccording to the invention shown in FIG. 3 has a second return line 65into the low-pressure region of the fuel supply system, which branchesoff from the cavity containing the closing spring element 67 above theinjection valve element 34. In the depiction according to FIG. 3, thereference numeral 68 indicates the stop point at which, with furtherpressure-relief of the control chamber 21, the end surface 62 of theinner, first valve element 28.1 comes to rest against the outer, secondvalve element 28.2 and carries it along with it in the openingdirection.

The remaining components of the fuel injector 4 according to theembodiment version shown in FIG. 3 that are not discussed in detailabove essentially correspond to the components that have already beendescribed in the embodiment version of the fuel injector according tothe invention in FIGS. 1 and 2.

FIG. 4 shows an embodiment version of a pressure booster that isactuated by an injection valve element, with two valve elements, one ofwhich is embodied as spring-loaded.

From the high-pressure source 1, the high-pressure inlet 2 extends via ahigh-pressure line branch 7 that contains a check valve 8 and via afirst parallel branch 1 1 and an additional parallel branch 12 to thecontrol chamber 15 of the pressure booster 3. In addition, thehigh-pressure source 1, which is embodied for example as a high-pressureaccumulator (common rail), acts on the working chamber 14 of thepressure booster 3 directly. The working chamber 14 and the controlchamber 15 of the pressure booster 3 are separated from each other by apiston unit 17, the end surface of the piston unit 17 oriented towardthe working chamber 14 having a larger diameter than the end surface ofthe piston unit 17 that delimits the compression chamber 18 of thepressure booster 3. The compression chamber 18 inside the injector body5 of the fuel injector 4 has a compression chamber line 20 branching offfrom it, which unites with the high-pressure line 7 containing the checkvalve 8 and transitions into the nozzle chamber inlet 9.

The control chamber 21 inside the fuel injector 4 is acted on withpressure via a high-pressure branch 22 with an inlet throttlerestriction 23 and can be pressure-relieved into the low-pressure return26 via an outlet throttle restriction 24 through actuation of a controlvalve 25.

A multi-part valve element 28 is also used in the embodiment version ofthe fuel injector 4 shown in FIG. 4. The multi-part valve element 28that acts on the injection valve element 34 in the nozzle body 6 of thefuel injector 4 includes a first valve element 28.1 whose end surface 62delimits the control chamber 21. The first valve element 28.1 has apiston extension 66 whose bottom end surface rests against the endsurface of the injection valve element 34. The first valve element 28.1is encompassed by a second, additional valve element 28.2; a continuousgap 72 is provided between the first valve element 28.1 and the secondvalve element 28.2. By contrast with the embodiment version shown inFIG. 3, the second valve element 28.2 does not delimit the controlchamber 21, but is instead disposed underneath the first valve element28.1 and its annular surface 60 is acted on by a spring element 70. Thespring element 70 rests against the top 71 of the valve chamber 63 inthe nozzle body 6 of the fuel injector 4.

The spring element 70 contained in the valve chamber 63 presses thecontrol edge 30 of the second, sleeve-shaped valve element 28.2 into itsclosed position so that the valve seat between the control edge 30 andthe housing edge 31 of the valve chamber 63 is closed in the idleposition and the pressure booster 3 is deactivated. Since the controledges 30 on the second valve element 28.2 and the control edge 31 on thevalve chamber 63 close the seat, it is not possible for the pressure inthe control chamber 15 to be relieved into the valve chamber 63 via theline 19 so that the piston unit 17 between the working chamber 14 andthe control chamber 15 of the pressure booster 3 is disposed in itsstarting position. A corresponding pressure shoulder inside the valvechamber 63 can serve to generate a closing hydraulic compression forcein order to increase the closing force on the control edge 30.

After the triggering of the control valve 25, which is preferablyembodied as a 2/2-way control valve, a pressure-relief occurs in thecontrol chamber 21 so that the end surface 62 of the first valve element28.1 travels into this chamber. If the control chamber 21 above the endsurface 62 of the first valve element 28.1 is pressure-relieved untilthe end surface of the injection valve element 34 comes to rest againstthe lower annular surface of the second valve element 28.2, i.e. if thestroke distance h₁ (reference numeral 32) is exceeded, then theinjection valve element 34 activates the pressure booster 3 since thehydraulic force acting on the pressure shoulder 35 in the nozzle chamber36 opens the sealed seat between the control edges 30 on the secondvalve element 28.2 and the control edge 31 of the valve chamber 63, anda pressure decrease in the control chamber 15 of the pressure booster 3can occur via the line 19 leading into the first low-pressure return 64.As a result, the fuel compressed in the compression chamber 18 of thepressure booster 3 is supplied to the nozzle chamber 36 via thecompression chamber line 20, the nozzle chamber inlet 9, and thejunction point 37 at which the nozzle chamber inlet 9 adjoins the nozzlechamber 36. With an appropriate pressure-relief of the control chamber21 of the injection valve element 34 within certain limits, i.e. so thatthe retraction path of the injection valve element 34 is less than thestroke distance h₁ (reference numeral 32), the design shown in FIG. 4can produce preinjections at the pressure level prevailing in thehigh-pressure source 1; a longer-lasting pressure-relief of the controlchamber 21 above the injection valve element 34 activates the pressurebooster 3 and a main injection phase with rate-shaping can be executedat an increased pressure level. In accordance with the triggering cycleof the control valve 25, one or more preinjection phases can beexecuted, depending solely on the triggering times and the triggeringprogram of the control valve 25, which preferably can be embodied as a2/2-way valve. In the embodiment versions proposed according to theinvention and shown respectively in FIGS. 1 and 2 and in FIGS. 3 and 4,with less than a certain needle stroke h₁ (reference numeral 32), aninjection of fuel into the combustion chamber 41 of an autoignitioninternal combustion engine can be executed at a first pressure levelthat corresponds, for example, to the pressure level of a high-pressuresource 1. Once the needle stroke h₁ (reference numeral 32) is exceeded,the injection valve element 34 activates the pressure booster 3 so thata subsequent injection then occurs at an increased pressure level. Onthe one hand, this permits the production of a boot-shaped injectionsince the first injection phase (preinjection) occurs at a lowerpressure level than the subsequent main injection. The activation of thepressure booster 3 through the vertical stroke motion of the injectionvalve element 34 causes an increased pressure level to occur atprecisely the moment required in terms of process engineering, inaccordance with the combustion progression occurring in the combustionchamber 41 of the autoignition internal combustion engine. In the rangeof small injection quantities, the injection valve element 34 can carryout a preinjection by executing a pressure-relief of the control chamber21, this pressure-relief being controlled with regard to its reliefduration in such a way as not to exceed the stroke distance h₁(reference numeral 32) so that the pressure booster 3 remainsdeactivated. The design proposed according to the invention cantherefore execute any number of preinjections at a pressure level thatis low in comparison that which is produced when the pressure booster 3is activated, thus allowing the fuel injector 4 according to the designproposed according to the invention to be operated with only one controlvalve 25.

Reference Numeral List

-   1 high-pressure source (common rail)-   2 high-pressure inlet-   3 pressure booster-   4 fuel injector-   5 injector body-   6 nozzle body-   7 high-pressure line-   8 check valve-   9 nozzle chamber inlet branch-   10 filling valve-   11 first parallel branch-   12 second parallel branch-   13 throttle restriction-   14 working chamber-   15 control chamber-   16 spring element-   17 piston unit-   18 compression chamber-   19 control line for control chamber-   20 compression chamber line-   21 control chamber-   22 high-pressure branch to control chamber-   23 inlet throttle restriction-   24 outlet throttle restriction-   25 control valve (2/2-way valve)-   26.1 first low-pressure return-   26.2 second low-pressure return-   27 one-piece valve element-   28 multi-part valve element-   28.1 first valve element-   28.2 second valve element-   29 end surface of one-piece valve element-   30 control edge of valve element-   31 control edge of housing-   32 stroke distance h₁-   33 annular chamber of valve element-   34 injection valve element-   35 pressure shoulder-   36 nozzle chamber-   37 junction point of nozzle chamber inlet-   38 annular gap-   39 injection opening-   40 seat at end oriented toward the combustion chamber-   41 combustion chamber-   42 closed injection opening-   50 low-pressure connection-   51 injection valve element 34 (retracted position)-   52 open injection openings-   60 annular surface of second valve element-   61 opening-   62 end surface of first valve element-   63 valve chamber-   64 first return line-   65 second return line-   66 piston extension-   67 closing spring-   68 stop of first valve element on second valve element-   70 spring element for second valve element-   71 stop for spring element-   72 overflow gap

1-17. (canceled)
 18. In a device for injecting fuel into a combustion chamber (41) of an internal combustion engine, comprising an injector body (5, 6), which contains an injection valve element (34) that can be actuated by a pressurization/pressure relief of a control chamber (21) executed by a control valve (25), and a pressure booster (3) that has a piston unit (17), which divides a working chamber (14) from a control chamber (15) and acts on a compression chamber (18) that communicates (9, 20) with a nozzle chamber (36) encompassing the injection valve element (34), the improvement wherein the pressurization (2, 11, 12)/pressure relief (19, 26, 64) of the control chamber (15) of the pressure booster (3) occurs as a function of the stroke motion of the injection valve element (34).
 19. The device for injecting fuel according to claim 18, further comprising a valve element (27, 28) that can move inside a hydraulic chamber (33, 63), which is fed by a control line (19) leading from the control chamber (15) of the pressure booster (3), the injection valve element (34) being associated with the valve element (27, 28).
 20. The device for injecting fuel according to claim 19, wherein the valve element (27, 28) disposed inside the hydraulic chamber (33, 63) acts on the end surface of the injection valve element (34) oriented away from the injection openings (39) disposed at the end oriented toward the combustion chamber.
 21. The device for injecting fuel according to claim 19, further comprising a surface (29, 60, 62) of the valve element (27, 28), which surface can be acted on hydraulically, protrudes into a control chamber (21) that exerts pressure on the injection valve element (34).
 22. The device for injecting fuel according to claim 19, wherein the valve element (27) is comprised of one piece and has a control edge (30) that forms a sliding seal with a control edge (31) in the hydraulic chamber (33).
 23. The device for injecting fuel according to claim 19, further comprising a return line (26.2, 64) branching from the hydraulic chamber (33, 63), which return line leads into the low-pressure region.
 24. The device for injecting fuel according to claim 22, further comprising a return line (26.2, 64) branching from the hydraulic chamber (33, 63), which return line leads into the low-pressure region, and wherein with a stroke motion of the injection valve element (34), which is triggered by a pressure-relief of the control chamber (21) and is shorter than a stroke distance h₁ (32) at which the control edges (30, 31) overlap, the sliding seal (30, 31) remains closed and an injection of fuel into a combustion chamber (41) occurs at a first pressure level.
 25. The device for injecting fuel according to claim 22, further comprising a return line (26.2, 64) branching from the hydraulic chamber (33, 63), which return line leads into the low-pressure region, and wherein with a stroke motion of the injection valve element (34), which is triggered by further pressure-relief of the control chamber (21) and exceeds the stroke distance h₁ (32), the control chamber (15) of the pressure booster (3) can be connected to the second low-pressure return (26.2) via the control line (19) and the open control edges (30, 31) and an injection of fuel into a combustion chamber (41) occurs at a second, higher pressure level.
 26. The device for injecting fuel according to claim 19, wherein the valve element (28) is comprised of multiple parts and has a first valve part (28.1) and a second valve part (28.2), at least one of which is acted on by the pressure prevailing in the control chamber (21) of the injection valve element (34).
 27. The device for injecting fuel according to claim 26, wherein the first valve part (28.1) is guided in the second valve part (28.2) and a stroke distance h₁ (32) is established between an end surface (29) of the first valve part (28.1) and a stroke stop (68) of the second valve part (28.2).
 28. The device for injecting fuel according to claim 27, wherein the second valve part (28.2) has a control edge (30) that cooperates with a sealing seat in the hydraulic chamber (63).
 29. The device for injecting fuel according to claim 27, wherein the second valve part (28.2) has a control edge (30) that cooperates with a sealing seat in the hydraulic chamber (63), and wherein, when the control chamber (21) is pressure-relieved, the first valve part (28.1) travels the stroke distance h₁ (32) toward the stop (68) and the injection valve element (34) executes an injection of fuel into the combustion chamber (41) at a first pressure level.
 30. The device for injecting fuel according to claim 27, wherein the second valve part (28.2) has a control edge (30) that cooperates with a sealing seat in the hydraulic chamber (63), and wherein with further pressure-relief of the control chamber (21), after the first valve part (28.1) travels the stroke distance h₁ (32), opening the second valve part (28.2) at the sealing seat in the hydraulic chamber (63), the control chamber (15) is pressure-relieved into the low-pressure side via the control line (19) and the hydraulic chamber (63), and an injection of fuel occurs at a second, higher pressure level.
 31. The device for injecting fuel according to claim 26, further comprising a spring element (70) acting on one of the valve parts (28.1, 28.2) of the multi-part valve element (28) in the direction of a sealing seat in the hydraulic chamber (63).
 32. The device for injecting fuel according to claim 26, further comprising a spring element (70) acting on one of the valve parts (28.1, 28.2) of the multi-part valve element (28) in the direction of a sealing seat in the hydraulic chamber (63), and a piston extension (66) of the first valve part (28.1) which passes through the second valve part (28.2) and forming an annular gap (72) with it, and the piston extension (66) of the first valve part (28.1) acting on the end surface of the injection valve element (34).
 33. The device for injecting fuel according to claim 26, further comprising a spring element (70) acting on one of the valve parts (28.1, 28.2) of the multi-part valve element (28) in the direction of a sealing seat in the hydraulic chamber (63), and wherein a stroke distance h₁ (32) between the second valve part (28.2) and the injection valve element (34) can be established, by which the injection valve element (34) can be moved with pressure-relief of a control chamber (21) in order to inject fuel at a first pressure level.
 34. The device for injecting fuel according to claim 26, wherein a spring element (70) acting on one of the valve parts (28.1, 28.2) of the multi-part valve element (28) in the direction of a sealing seat in the hydraulic chamber (63), a stroke distance h₁ (32) between the second valve part (28.2) and the injection valve element (34) can be established, by which the injection valve element (34) can be moved with pressure-relief of a control chamber (21) in order to inject fuel at a first pressure level and wherein a stroke distance h₁ (32) between the second valve part (28.2) and the injection valve element (34) can be established, by which the injection valve element (34) can be moved with pressure-relief of a control chamber (21) in order to inject fuel at a first pressure level, and wherein with further pressure-relief of the control chamber (21) and an opening movement of the injection valve element (34) that exceeds the stroke distance h₁ (32), the injection valve element (34) moves the second valve part (28.2) away from its seat in the hydraulic chamber (63) and pressure-relieves the control chamber (15) of the pressure booster (3) into the low-pressure side via a control line (19) so that an injection of fuel into the combustion chamber (41) occurs at a second, higher pressure level. 